This invention relates generally to the monitoring of a liquid level within a reservoir and specifically to such monitoring utilizing a type of static-tube level sensor and more specifically to such monitoring wherein the liquid is a molten alloy.
Extruding a molten alloy from a pressurized crucible through an extrusion nozzle onto a rotating chill surface is one of several technologically significant methods available for the continuous casting of continuous glassy alloy filaments, as representatively shown in U.S. Pat. No. 4,142,571 "Continuous Casting Method for Metallic Strips" issued Mar. 6, 1979 to M. Narasimhan.
The degree of transverse dimensional constancy along the length of the filament is sensitive to variations in the stream of extruded melt impinging upon the rotating chill surface and therefore sensitive to extrusion pressure at the extrusion nozzle. Nozzle pressure is determined by the total effect of the static head of the molten alloy above the nozzle and the gas over-pressure within the pressurized crucible. Thus, to maintain a substantially constant nozzle pressure during extrusion, either a compensating molten alloy flow to the crucible must be provided or the pressurization of the crucible must be increased accordingly. In either situation, it is fundamental to monitor the level of the molten alloy in the crucible.
It is known to use pressure-tube devices to sense a liquid level. These devices are attractive for such use owing primarily to their simplicity. However, substantial materials problems are frequently encountered in applying these devices for sensing the level of a high temperature, molten material. There are basically two types of pressure-tube level sensors: the static-tube in combination with an immersible diaphragm, wherein the differential pressure between the static head in the liquid and the tube pressure causes deflection of the diaphragm membrane which is correlated with liquid level; and the bubbler-tube, wherein one opening of the tube is placed in the liquid and a flow of gas is passed through the tube with the resulting back-pressure being correlated to the liquid level. The static-tube with diaphragm device is not suitable for immersion in a molten material as the high temperature environment likely will cause destruction of the diaphragm or, at the least, contamination of the melt. The bubbler-tube may be unsatisfactory where the bubbling action interferes with the particular metallurgical process, especially in a small scale, sensitive process, for example by gas bubbles being entrained in the extruded flow of the above described filament casting process.
The present invention overcomes these limitations by utilizing only a static-tube whereby the meniscus of the liquid in the static-tube essentially acts as a diaphragm.